Finley's pumpkin had a mass of $6.5$ kilograms $(\text{kg})$ before he carved it. After carving it, the pumpkin had a mass of $3.9\,\text{kg}$. What was the percent decrease in the mass of the pumpkin?
Solution: Let's start by finding the amount of decrease in the mass. $6.5\,\text{kg}-3.9\,\text{kg}=2.6\,\text{kg}$ What percent of $6.5$ kilograms is $2.6$ kilograms? We can rewrite that question as an equation. $\begin{array}{ccccc} {\text{what percent}}&\text{of}&{6.5\,\text{kg}}&\text{is}&2.6\,\text{kg}\\\\ {?\%}&\times &{6.5}&=&2.6 \end{array}$ Let's solve for the percent. $\begin{aligned} \dfrac{{?\%}\times {6.5}}{6.5}&=\dfrac{2.6}{6.5}\\\\ {?\%}&={0.4} \end{aligned}$ Percent means per hundred, so ${0.4}$ is equivalent to ${\dfrac{40}{100}}$ and also to ${40\%}$. There was a $40\%$ decrease in the mass of the pumpkin.